1. Study of Prompt Dimuon and Charm Production with Proton and Heavy Ion Beams at the CERN SPS The NA60 experiment Carlos Lourenço and Gianluca Usai on behalf of the NA60 Collaboration Reminder of the physics motivation and plans of NA60 Evolution with respect to the proposal –Experimental apparatus –Readout electronics, DAQ and detector control

2. Excess production of intermediate mass dimuons NA38+NA50 The p-A data is properly described by Drell-Yan and charm decays The required charm cross-section agrees with previous direct measurements In heavy ion collisions the yield of produced dimuons exceeds the expected sources The excess increases with the centrality of the nuclear collisions NA50

3. Charm enhancement ? The measured yields can be reproduced by scaling up the expected charm contribution by up to a factor 3 L. Capelli, NA50, at QM2001

4. Thermal model of Rapp and Shuryak (central collisions only) explicit introduction of a QGP phase Integration over space-time history : fireball lifetime : 14 fm/c initial temperature : T i = 192 MeV critical temperature : T c = 175 MeV Thermal dimuons production ? L. Capelli, NA50, at QM2001 The measured yields can also be reproduced by adding thermal radiation to the Drell-Yan and open charm sources   ++    - -

5. Low mass dilepton production The p-Be and p-Au data are properly described by the standard cocktail of hadronic decays but there is an excess in the Pb-Au data ! The excess increases with the square of the charged particle multiplicity and is more pronounced at low p T Chiral symmetry restoration ? Better statistics, signal to background ratio and mass resolution are needed !

6. J/  suppression in S-U and Pb-Pb (1987-1998) melting of  c ? melting of direct J /  ? Color screening prevents charmonia formation in a deconfined medium. Binding energies :  ’  50 MeV,  c  250 MeV, J/   650 MeV The thresholds are only visible in the Pb-Pb data !  A new collision system is needed to check onset PLB 477 (2000) 28 NA50 QM2001

7.  ’ suppression in S-U collisions melting of  ’ ? Drop by factor ~ 3 The  ’ suppression pattern is very different between p-A and S-U data ! Color screening ? If so, what is the  ’ melting temperature (  value of T c ) ?  A new collision system is needed with points below and above L = 4-5 fm

8. Physics motivation  What is the origin of the intermediate mass dimuon excess ? Thermal dimuons ?  Is the open charm yield enhanced in nucleus-nucleus collisions ?  Is the  meson modified by the medium ?  observe the  reference peak !  What is the physics variable that rules the onset of J/  suppression ?  What is the physical origin of the  ’ suppression ? Color screening ?  What fraction of J/  come from  c decays ? What is the nuclear dependence of  c production in p-A collisions ?

9. Detector concept Track matching through the muon filter Improved mass resolution Improved signal / background ratio (rejection of  and K decays) Improved systematical uncertainties (vertex reconstruction) Muon track offset measurement Separate charm from prompt (thermal) dimuons     D  { offset vertex Adding silicon detectors to track the muons before they traverse the hadron absorber Improved measurement of prompt dimuon production and open charm in heavy ion collisions

10. The silicon vertex spectrometer proposed in P316 10 planes 88 pixel readout chips 720 000 channels pixel size : 50  425  m 2 Silicon pixel telescope 1.7 T dipole field 2 x-y stations of  -strip Si detectors at T = 130 K ~ 20  m resolution on the transverse coordinates of the beam ions Beamscope

11. Dimuon mass resolution : simulation Clear improvement in mass resolution and signal / background ratio  M at M = 1 GeV : 70 MeV in NA50  20 MeV in NA60 NA50 NA60 Vertex spectrometer with pixels without pixels J/  ’’ 

12. 4 “half” planes 33 LHC1 chips ~ 60’000 channels 1998 feasibility tests absorber target pixel box TC8 magnet 1.7 T dipole magnetic field

13. Dimuon mass resolution : April 1998 data few hours at ~ 10 8 protons / burst on a 10 mm Be target half acceptance, bump-bonding, radiation damage  low detector efficiency only 600 dimuon events in the final analysis data sample without pixels  M = 70 MeV with pixels  M = 20 MeV

14. Measurement of the muon track offset Determination of the interaction vertex Impact parameter of the muon tracks D + : c  = 317  m D 0 : c  = 124  m D

15. IMR excess : charm or thermal dimuons ? Prompt dimuons selection : events with muon track offset < 90  m Charm selection : events with muon track offset in the range 90  800  m and muons > 180  m away from each other in the transverse plane at z v

16.  c production in p-Be and p-Pb photon converter 4 Be and 1 Pb targets; ~ 30 days of protons Background subtracted by mixing J/  and e + e  pairs from different events  c         e + e  What fraction of J/  ’s come from  c decays ? Does it change from p-Be to p-Pb ? B = 1.7 T

17. Developments since the proposal Offline software advancing well : AliRoot framework, from Fortran to C++ Beamscope tested in Sept. - Nov. 2000 : 42 days of high intensity Pb beam New detector : beamscope for proton running, with new fast amplifier chip New target dipole magnet : higher field ; much better integration of detectors Better detectors to reject bad triggers : quartz blade, interaction counter, P2 New gas system for the muon chambers New readout electronics and DAQ : increased bandwidth We benefit from the critical help provided by the ALICE offline software team, the RD39 collaboration and the cryo lab, the EP-MIC group, W. Flegel and F. Bergsma, the LHC gas group (F. Hahn et al.), the EP-ED group and the EP-AID group

18. Status of the offline software Detector setup : The whole detector geometry and materials are described using GEANT Event generation : Soft signals with Genesis code (thermal distributions) Hard processes with PYTHIA Underlying hadronic background with VENUS Algorithms : Trigger logic implemented Detector response done up to the hit level Track and vertex reconstruction under development Everything must be ready for the October 2001 run

19. The beamscope detector Cryogenic Module Amplifier Cards 200 mm Vacuum chamber CCE (in %) Heavily irradiated silicon detectors continue working when operated at cryogenic temperatures beam

20. Beamscope test in November 1999 Exposed for 3 days to the 40 A GeV Pb beam Average beam intensity: 5  10 6 ions per 4.5 s burst Total dose: ~ 1 Grad

21. Beamscope test in Sept.-Nov. 2000 Exposed 42 days in the NA50 Pb beam Average beam intensity: 7  10 7 ions per 4.5 s burst Total fluence : 5 ± 2  10 14 ions / cm 2 ( 90 ± 40 Grad ) Electronics suffered from radiation in the beam area

22. Pb ion signal shape 8 Gs/s time (ns) amplitude (mV) 200 V 2 Gs/s time (ns) amplitude (mV) 200 V Very fast rise time ( < 500 ps) Long tail (~ 20 ns) Shaping (signal width ~ 4 ns) improves double-pulse resolution Signal is broader Amplitude ~ 20 times lower but still visible ! Non-irradiated After ~ 40 Grad

23. Beam profile and cluster correlations hits (  10 3 ) strip number Day 38 1.2 mm hits (  10 3 ) Time accuracy of the readout electronics system integrating all the strips over several spills  = 1.0 ± 0.1 ns Day 42 y 2 (  m) y 4 (  m) Correlation of clusters in the 2 vertical measurements

24. Beamscope for proton running Chip CERN_NA60_32_ch Measuring the interaction point with few prompt tracks ~ 100 % sub-target reconstruction efficiency Improved Z and X-Y vertex resolutions Increased tagging efficiency for D mesons and prompt muons New CMOS readout chip for the proton beamscope 32 channels ; runs at around T = 130 K Simulated double peak resolution : 10 ns at room T High gain : 1 mip = 60 mV Power dissipation = 275 mW Design submitted for production Tests and module assembly start mid June Use on the beam in October 2001

25. Improvement in the vertex magnet The new dipole magnet, PT7, has a field of 2.5 T (for I = 900 A). The mass resolution of the  c peak, dominated by the momentum measurement of the electron and positron tracks, improves from 43 MeV to 25 MeV. The signal to background ratio improves by around factor of 2. The integration of the detectors is much easier than with TC8. Field along beam axis

26. NA60 target region Front view PT7 Beamscope modules at 45 degrees BeO absorber The integration and installation studies have started, including mechanical supports, alignment, cooling systems, vacuum, readout cables, etc. Care must be taken with the strong magnetic field and the high radiation load.

27. Critical concerns The NA60 physics program relies heavily on the intermediate mass ion beam  Indium-Indium collisions should be available as soon as possible The operation of the muon spectrometer demands the support of IN2P3 The construction of the silicon vertex spectrometer and the successful operation of NA60 requires a strong CERN participation  The NA60 collaboration is weaker than anticipated one year ago Successive time delays in the availability of the Alice1 pixel readout chips Only around 15 good assemblies are expected per wafer  Silicon pixel telescope will not be ready before the ion run of 2002

28. Silicon microstrip telescope for proton physics Each detector is one wafer; inner part = A-D zones; outer part = E-F zones Only the ~ 300  m thickness of the sensors on the way of the particles Small detectors (only inner part is read) = 384 channels per half plane Big detectors (all strips are read) = 768 channels per half plane One readout chip, SCTA3, reads 128 strips Full telescope = 4 small and 3 big X-Y stations = 120 readout chips One hybrid (3 or 6 chips) and DAQ adapter card per half plane; total = 28 14 ADC cards, 6 channels each (3 ADCs per hybrid) Data rate around 30 Mbyte per burst ; 2 PCI-FLIC cards needed in 1 PC Requires only 28 working pixel chips to build 3 small and 1 big pixel planes 6.5 charged particles per average p-Pb collision : less than 2 or 3 % occupancy Resolution in impact parameter of muon tracks is around 25  m

29. VME readout electronics for pixel telescope 2 VME crates VME to PCI MXI-2 interface  20 Mbyte/s 721 000 channels Limitations :  required bandwidth beyond VME limit (12 Mbyte/s)  number of events / burst limited to 4000  non scalable system  bad ratio performance / cost (VME crates)  pixel chips readout frequency limited to  10 MHz 64 pixel chips 24 pixel chips VME Pilot board Zero sup 32 bit FIFO Hit encoding 20 bit FIFO VME VME bus pixchip

30. Readout of muon chambers and trigger hodoscopes 22 RMH modules / crate System encoder  16 bit words To VME buffer 4 Mbyte Cascaded CAMAC crates RMH 32 hit channels 20 000 channels Limitations :  memory limit on the RMH to VME interface buffer : 4 Mbyte  slow word transmission protocol (500 ns)  number of events / burst < 4000

31. PCI - FLIC readout electronics PCI - FLIC card Mezzanine outline User connector ; 46 signals for pixel data Pixel Readout Board (PCI mezzanine card) To / from front-end electronics (LVDS) FPGA on PRB Mezzanine area F I F O 32 Mbyte spill-buffer PCI bus  100 Mbyte/s RAM Zero suppression & hit encoding - pixel chips readout control F I F O

32. PCI readout electronics for the pixel telescope PCI cards (up to 5 cards per PC motherboard) Local data concentrators (under DATE software control) Parallel readout scalable system 74 Mbyte/s Linux PCs

33. Pixel telescope data throughput 10 K x 16 bit words  20 Kbyte / event PCI : 20 Kbyte / event @ 74 Mbyte / s   270  s to acquire one event VME : 20 Kbyte / event @ 20 Mbyte / s   1000  s to acquire one event Pixel plane number Average hit number Small planes Large planes

34. Pixel telescope readout performance Pixel chip : 4 Event Buffers VME : 1000  s / event pixCLK @ 10 MHz PCI : 270  s / event pixCLK @ 20 MHz We can take ~ 8000 events on tape / burst with less than 10 % dead time MultiEvent Buffer : dead time  1/4 of SingleEvent Buffer triggers per second dead time

35. PCI readout electronics for RMH RMH cable adapter mezzanine RMH NIM signals ECL  TTL converters Differential 2*22 ECL 32 MB spill-buffer RMH cable handshake Word cycle 350 ns  6 MB/s bandwidth 16 bit word handshake 10..15 sec readout from burst buffer5 sec fill buffer

36. Muon spectrometer readout performance   320 (16 bit) words / event   0.7 Kbyte / event  RMH  PCI buffer bandwidth  6 Mbyte / s NA50 NA60 dead time triggers per second NA50 : 500 ns/word x 320 words = 160  s one partition : 160  s service time 700 triggers/s, with 10 % dead time, spill of 5 s :  3150 events on tape / burst NA60 : 350 ns/word x 320 words = 100  s two partitions : 50-60  s service time 1800 triggers/s, with 10 % dead time, spill of 5 s :  8000 events on tape / burst 10 %

37. From VME to PCI detector readout : summary General :  easy readout partitioning (up to 5 PCI cards per PC)  PCI spill-buffer directly mappable into the DAQ software Pixel detector :  PCI cards readout in parallel (sequential readout with VME)  74 Mbyte/s bandwidth (20 Mbyte/s with VME)  pixel chips clocked @ 10 - 20 - 40 MHz (on board PLL) Muon spectrometer :  PCI spill buffer increased to 32 Mbyte (4 Mbyte with VME)  hit readout time 350 ns (500 ns with VME)

38. The data acquisition system 60 MB/burst80 MB/burst1.2 MB/burst8 MB/burstTotal: 150 MB/burst FastEthernet  11 MB/s GbitEthernet  110 MB/s All nodes : Linux/DATE Run control Beam area LDC pix2 LDC pix1 0.12 MB/s0.8 MB/s 8 MB/s Fast/Gbit switch 3+4 PCI-FLIC/PRB Online monitoring GDC tape Disk server LDC BS+ZDCLDC MS 6 MB/s 15 MB/s DAQ software DATE

39. The detector control system Pixel cooling Tmon (20 chan) Interlock (2 chan) Cryo flows Cryo/pixel control Gas control mixer distributor Gas PLC Permanent storage CAEN SY2527CAEN SY403 HV, LV pixels HV, LV beamscope HV ZDC (2 crates) HV hodoscopes (14 crates) CAEN frontend (Linux) PVSS/SCADA with OPC (WinNT)

40. Summary NA60 will clarify the origin of the intermediate mass dimuon excess and measure the yield of charmed mesons produced in heavy ion collisions. Considerable technical improvements were made since the proposal : new detectors, new vertex magnet, new readout electronics and DAQ, etc. Severe lack of resources (people and budget) keep the collaboration much weaker than anticipated. Stronger support from CERN and other institutes is mandatory to allow the experiment to take good physics data in 2002. Data with good statistics, mass resolution and signal to background ratio will allow to study the production of ,  and  mesons, as well as the charmonia resonances.

41. The NA60 Collaboration Brookhaven R. Arnaldi, A. Baldit, K. Banicz, K. Borer, L. Casagrande, J. Castor, B. Chaurand*, W. Chen, B. Cheynis, P. Chochula, C. Cicalò, M.P. Comets, P. Cortese, V. Danielyan, A. David, A. De Falco, N. De Marco, A. Devaux, B. Dezillie, L. Ducroux, B. Espagnon, P. Force, E. Gangler, V. Granata, A. Grigorian, S. Grigorian, J.Y. Grossiord, A. Guichard, H. Gulkanian, R. Hakobyan, E. Heijne, M. Hess, P. Jarron, D. Jouan, L. Kluberg*, Y. Le Bornec, B. Lenkeit, Z. Li, C. Lourenço, M.P. Macciotta, M. Mac Cormick, F. Manso, D. Marras, A. Masoni, S. Mehrabyan, H. Muller, A. Musso, A. Neves, B. Pes, S. Popescu, G. Puddu, P. Ramalhete, P. Rosinsky, P. Saturnini, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, E. Siddi, P. Sonderegger, G. Usai, G. Vandoni, H. Vardanyan, N. Willis, H. Wöhri and M. Zagiba Lisbon Orsay CERN Bern Bratislava Torino Yerevan Cagliari Lyon Clermont 11 institutes but very few financing agencies *) personal commitment